The present invention relates to an assembly of the type comprising a printed circuit card and a sole plate forming a heat sink, which are arranged on a base forming a radiator.
In an assembly of this type, the printed circuit card is conventionally a double-sided card which has metallized holes TM, as illustrated in FIG. 1.
These metallized holes TM constitute what are called xe2x80x9cthermal viasxe2x80x9d which, in addition to the electrical interconnection between the two sides of the substrate, allow heat to be transferred between the bass and the heat-dissipating components with which the card is equipped.
However, the amount of heat which these holes can transfer is small. The reason for this is that, even though the thermal conductivity of copper is about 1000 times higher than that of the epoxy materials used to produce the substrates of the printed circuit cards, the thickness of the copper layers deposited on the walls of the holes which pass through the substrates is very small (of the order of 30 xcexcm) so that little heat is transferred.
In an assembly of one or more components on a printed circuit card having thermal vias, the document U.S. Pat. No. 5,646,826 proposes to increase the heat-transfer capacity of these holes by injecting into them a material whose thermal dissipation properties are superior to those of the printed circuit card forming the substrate. Injection solutions of this type are generally expensive and require the use of specific and elaborate tools.
In an assembly of one or more components on a printed circuit card, the document DE-A-196 01 649 proposes to replace some of the printed circuit card by a bulk metal part which is more conductive than the printed circuit card. Using a bulk metal part causes problems with the flatness of the assembly and subjects the printed circuit card to significant lateral stresses.
The solutions employed in the prior art have a number of drawbacks which need to be resolved.
It is therefore an object of the invention to provide an assembly with a heat sink which allows better heat transfer between the metal base of the boxes of the power components supported by the printed circuit card and the base, by means of a heat sink which permits better cooling or better thermal dissipation for the electronic card.
To that end, the invention proposes an assembly supported on a base forming a radiator or capable of being mounted on such a base, comprising a printed circuit card which has in its thickness a plurality of a holes intended to transfer heat between one face of the said printed circuit card, which supports one or more electronic components each enclosed by a box, and the base forming a radiator, having a plurality of pads a which are made of a thermally conductive material and pass through the printed circuit card over substantially its whole thickness while being housed by the holes therein, in order to transfer heat between one face of the printed circuit card, which supports one or more components, and the base, the pads (4a) are integral with a plate (4), referred to as the sole plate, which supports them, characterized in that the sole plate (4) is interposed between the printed circuit card (1) and the base.
The invention is advantageously supplemented by the various characteristics below, taken individually or in any of their feasible combinations:
the sole plate is made of the same material as the bottom of the component box or of a material with equivalent coefficient of expansion and/or thermal conductivity;
the assembly has a ductile thermal joint through which it is in contact with the base;
pads are directly supported by the box of electronic components and are in contact with the base through a ductile thermal joint;
the sole plate has complementary means capable of mechanically holding it to the card;
the complementary holding means are spikes which are supported by the sole plate;
the sole plate (4) and the pads (4a) are soldered to the card in order to spread the thermal dissipation;
the sole plate has through-holes for discharging the residual air possibly trapped in the solder.